Pearlizing agents are routinely added to personal care and household products to make the products pearly and silky. Ethylene glycol distearate or monostearate are commonly used pearlizing agents. These pearlizing agents generally do not have viscosity building effect; therefore, additional thickeners are needed in the formulation to prevent the formulation from becoming just an emulsion.
To generate a pearlizing effect, the pearlizing agents also need to have the appropriate crystal size, which are generally in microns. However, the ability to control the crystal size is limited. In using these pearlizing agents, the formulation is typically heated first to solubilize the pearlizing agents. Afterwards, the formulation is cooled down for the pearlizing agents to crystallize. In the heating step, the right solubilizing concentration needs to be used. If the solubilizing concentration is too high or too low, crystallization may not occur. In the cooling step, the cooling rate, flow rate and other parameters need to be monitored in order for the pearlizing agents to crystallize to the appropriate size. If the cooling rate is too fast, crystals may form too quickly and grow too large in size. If the cooling rate is too slow, the processing time will be prolonged, which will increase production costs. The stirring speed also needs to be controlled. During the solubilizing stage, at high temperatures fast stirring should be employed so the pearlizing agent can dissolve quickly. At the cooling stage, low stirring speed is preferred to help the crystallization process. The choice of surfactants can also affect the crystal formation and therefore the pearlizing effect. (Bolzinger et. al., Colloids and Surfaces A, Physicochemical and Engineering Aspects, 2007, 299, 93). Overall the process can be complicated and can result in inconsistencies in crystal size formation, and failure in generating a pearlizing effect.
Several methods have been introduced to overcome the problem. For example, a dispersion of ethylene glycol distearate in water is commercially available (Tego Pearl N 100, Tego Pearl N 300, Evonik Goldschmidt Corporation). These pearlizing agents can be used at room temperature without the need to heat the formulation. However, when the final formulation viscosity is low, the pearlizing agent can precipitates out of the system. Therefore, thickeners need to be added, which can increase the formulation cost.
Pearlizing concentrates were also mentioned in U.S. Pat. Nos. 5,646,106; 5,925,604; 6,165,955; and 7,578,995. The concentrates consist of ethylene glycol stearates, non-ionic surfactant (ethoxylated fatty alcohol), amphoteric surfactant (betain), glycol emulsifier and water. Such concentrates can be formulated with other ingredients at room temperature to generate a formulation with pearlizing effect. However, such a formulation does not have a good viscosity building effect. Cocamide diethanol amine (cocamide DEA) and other thickeners need to be added. Furthermore, the concentrate contains ethoxylated fatty alcohol, which limits their use in polyethylene glycol free applications.
Pearlizing concentrates were also mentioned in U.S. Patent Publication No. 20040110659, which described glycerol carbamates made by reaction of glycerol, diglycerol and/or polyglycerol carbonate with a primary and/or secondary amine. Such carbamates were found to be thickeners for cosmetic and pharmaceutical preparations. The materials were prepared by addition of fatty amines to glycerol carbonates. The hydrophilic impurities were removed by dichloromethane and extracted with hydrochloric acid. However, for cosmetic applications, dichloromethane is a toxic solvent, and its use should be avoided.
As such there is a need in the art for a pearlizing agent that is easy to use and that can be cost efficient in developing formulations. It is a further object of the present invention to provide a pearlizing agent that displays a viscosity building effect. These needs are satisfied by the present invention.